Methods of forming a package substrate

ABSTRACT

A coreless package substrate with dual side solder resist layers is disclosed. The coreless package substrate has a top side and a bottom side opposite of the top side and includes a single build-up structure formed of at least one insulating layer, at least one via, and at least one conductive layer. The coreless package substrate also includes a bottom plurality of contact pads on the bottom side, and a top plurality of contact pads on the top side. A bottom solder resist layer is on the bottom side, and a top solder resist layer is on the top side. The concept of dual side solder resist is extended to packages with interconnect bridge with C4 interconnection pitch over a wide range.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a divisional of U.S. patent application Ser.No. 15/596,968, filed May 16, 2017, which is a divisional of U.S. patentapplication Ser. No. 14/463,285, filed Aug. 19, 2014, now U.S. Pat. No.9,704,735, issued Jul. 11, 2017, entitled “SOLDER RESIST LAYERS FORCORELESS PACKAGES AND METHODS OF FABRICATION”, the entire disclosure ofwhich are hereby incorporated by reference in their entirety and for allpurposes.

TECHNICAL FIELD

Embodiments of the present invention relate generally to packagesubstrates. More particularly, embodiments of the present inventionrelate to coreless package substrates and substrate packages with widelyvarying C4 pitch with dual solder resist layers and their methods offabrication.

BACKGROUND

Coreless package substrates are important components for modernelectronic devices, such as integrated circuit dies. Coreless packagesubstrates interconnect integrated circuit dies to circuit boards andhelp reduce overall package assembly height. Typically, integratedcircuit dies mount directly to package substrates. As a result, packagesubstrates are required to be compatible with fine contact arrangementsof the integrated circuit dies. Recent technological advancement hasdeveloped package substrates that are compatible with the fine contactarrangements of integrated circuit dies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross-sectional view of a coreless packagesubstrate, in accordance with an embodiment of the invention.

FIG. 1B illustrates a cross-sectional view of a coreless packagesubstrate having contact pads of different widths on each side of thecoreless package substrate, in accordance with an embodiment of theinvention.

FIG. 2 illustrates a cross-sectional view of a package assemblyincorporating a coreless package substrate, in accordance with anembodiment of the invention.

FIGS. 3A-3I illustrate cross-sectional views of a method of forming acoreless package substrate by forming a bottom solder resist layerbefore removing a temporary substrate, in accordance with an embodimentof the invention.

FIGS. 4A-4H illustrate cross-sectional views of a method of forming acoreless package substrate by forming a bottom solder resist layer afterremoving a temporary substrate, in accordance with an embodiment of theinvention.

FIGS. 5A-5G illustrate cross-sectional views of a method of forming athick surface finish on contact pads of a coreless package substratehaving an embedded silicon bridge, in accordance with an embodiment ofthe invention.

FIG. 6 illustrates a computing system implemented with oneimplementation of the invention.

FIG. 7 illustrates a conventional coreless package substrate.

DETAILED DESCRIPTION

Coreless package substrates with dual solder resist layers and theirmethods of fabrication are disclosed. Embodiments of the presentinvention are described with respect to specific details in order toprovide a thorough understanding of the invention. One of ordinary skillin the art will appreciate that embodiments of the invention can bepracticed without these specific details. In other instances, well knownsemiconductor processes are not described in specific detail in order tonot unnecessarily obscure embodiments of the present invention.Additionally, the various embodiments shown in the figures areillustrative representations and are not necessarily drawn to scale.

Embodiments of the invention are directed to coreless package substrateswith dual solder resist layers and their methods of fabrication. In oneembodiment of the invention, the coreless package substrate includes abuild-up structure and top and bottom contact pads. The top contact padsare formed on a top side of the coreless package substrate, and thebottom contact pads are formed on a bottom side of the coreless packagesubstrate. In an embodiment, top and bottom surface finishes are formedon the top and bottom contact pads, respectively. The coreless packagesubstrate further includes a top solder resist layer disposed on the topside, and a bottom solder resist layer disposed on the bottom side. As aresult, the coreless package substrate has a layer of solder resist onboth the top and bottom sides.

The top and bottom solder resist layers enhance device performance byallowing integration of active/passive device components on both sidesof the coreless package substrates. Additionally, the top and bottomsolder resist layers reduce occurrences of pad-to-pad bridging byminimizing formation of solder residue on both sides of the corelesspackage substrates. Further, the top and bottom solder resist layersallow selective tuning of surface finish plating thicknesses by enablingdifferent surface finish thicknesses to be formed on contact padslocated on the coreless package substrates.

An exemplary conventional coreless package substrate is illustrated inFIG. 7. A conventional coreless package substrate 700 includes acoreless package substrate 702 and a single solder resist layer 708. Thesingle solder resist layer 708 is disposed on a top side 706 of thecoreless package substrate 702. Conventional coreless package substrates700 do not have a solder resist layer on a bottom side 704. The solderresist layer 708 enables contact pads disposed on the top side 706 to beformed with narrow widths for coupling to fine-pitched devicecomponents. As a result, only one side of a conventional corelesspackage substrate 700 can be integrated with fine-pitched devicecomponents.

FIG. 1A illustrates a coreless package substrate 100A with dual solderresist layers according to embodiments of the invention. Theillustration in FIG. 1A depicts a close-up view of a portion of anentire coreless package substrate 100A for clarity purposes. Thecoreless package substrate 100A includes a build-up structure 102containing an alternating arrangement of insulating layers 104 andconductive layers 106. The conductive layers 106 may be electricallycoupled to one another through the insulating layers 104 by vias 108. Inembodiments, the build-up structure 102 does not contain a stiffeningcore formed of a material different from the insulating layers 104 andconductive layers 106 of the build-up structure 102.

In an embodiment, the build-up structure 102 has a top side 112 and abottom side 110 opposite of the top side 112. The top side 112 may be acontrolled collapse chip connection (C4) side of the build-up structure102 that makes electrical connection with a device component, such as anintegrated circuit die. In an embodiment, the bottom side 110 may be asecond level interconnect (SLI) side of the build-up structure 102 thatmakes electrical connection with at least a second level interconnect,such as an interposer and a printed circuit board (PCB).

The coreless package substrate 100A further includes top contact pads124 and bottom contact pads 122. The top contact pads 124 are disposedon the top side 112 of the build-up structure 102, and the bottomcontact pads 122 are disposed on the bottom side 110 of the build-upstructure 102. The top and bottom contact pads 124 and 122 mayelectrically couple the coreless package substrate 100A to devicecomponents and/or second level interconnects. In embodiments, the topcontact pads 124 are electrically coupled to the bottom contact pads 122by conductive layers 106 and vias 108 of the build-up structure 102.

In embodiments, surface finishes are disposed on exposed surfaces of thetop and bottom contact pads 124 and 122. The surface finishes maypassivate exposed surfaces of the contact pads to prevent oxidation ofthe contact pads. In an embodiment, a top surface finish 120 may bedisposed on the top contact pads 124, and a bottom surface finish 118may be disposed on the bottom contact pads 122. In embodiments, the topand bottom surface finishes 120 and 118 are formed of a conductivematerial that does not substantially interfere with electrical signalsflowing into and out of the top and bottom contact pads 124 and 122,respectively. For instance, the surface finishes 120 and 118 may beformed of a metal, such as nickel (Ni), palladium (Pd), gold (Au),silver (Ag), and combinations thereof. In an embodiment, the surfacefinishes 120 and 118 are formed of a layer of Ni and a layer of PdAu ontop of the layer of Ni.

According to embodiments of the invention, the coreless packagesubstrate 100A further includes a top solder resist layer 116 and abottom solder resist layer 114. In an embodiment, the top solder resistlayer 116 is disposed on the top side 112, and the bottom solder resistlayer 114 is disposed on the bottom side 110. The solder resist layers116 and 114 may prevent pad-to-pad bridging by repelling solder-basedmaterials and prohibiting residue from remaining on the solder resistsurface during formation of interconnect structures (e.g., solderbumps). Prohibiting formation of solder residue allows narrower contactpads to be formed for electrical coupling to active/passive componentswith fine-pitched contact arrangements. Narrow contact pads enableformation of contact arrangements with fine pitches. As a result, thetop and bottom solder resist layers 116 and 114 may allow fine-pitchedcontact arrangements to be formed on both the top and bottom sides 112and 110, respectively.

For example, as depicted in FIG. 1A, the bottom contact pads 122 mayinclude wide contact pads 122A and narrow contact pads 122B. The widecontact pads 122A may be formed with a contact pitch suitable forinterconnection with SLI structures having wide contact pitches, such asa PCB or an interposer. The narrow contact pads 122B may be formed witha contact pitch suitable for interconnection with device components,such as an integrated circuit die. Pitch requirements may substantiallydictate the limits of pad widths. Accordingly, the widths of the wideand narrow pads 122A and 122B may vary according to pitch requirements.In an embodiment, the width of the wide pads 122A is at least 3 timeswider than the width of the narrow pads 122B. In an embodiment, thewidth of the wide pads 122A ranges from 300 to 400 μm and the width ofthe narrow pads 122B ranges from 80 to 100 μm. In an embodiment, thepitch of the wide pads 122A ranges from 600 to 800 μm and the pitch ofthe narrow pads 122B ranges from 160 to 200 μm.

The top contact pads 124 may also include wide contact pads 124A andnarrow contact pads 124B as shown in an exemplary coreless packagesubstrate 100B in FIG. 1B. The illustration in FIG. 1B depicts aclose-up view of a portion of an entire coreless package substrate 100Bfor clarity purposes. The wide contact pads 124A may have a width and acontact pitch suitable for coupling to device components, such asintegrated circuit dies. In an embodiment, the contact pitch of the widecontact pads 124A corresponds with the standard central processing unit(CPU) bump pitch. For example, in an embodiment, the wide contact pads124A a pitch in the range of 120 to 130 μm and a corresponding width inthe range of 80 to 90 μm.

The coreless package substrate 100B may include an embedded device 126within the build-up structure 102. The embedded device 126 may be anembedded interconnect bridge formed of a silicon, an organic, or a glassmaterial. Embedding a silicon bridge within the build-up structure 102may enable the coreless package substrate 100B to be suitable for highbandwidth applications. In an embodiment, the embedded device 126interconnects a CPU to a fine-pitched device, such as a memory chip. Thenarrow contact pads 124B may have a pitch that corresponds with the finecontact pitch requirement of the memory chip. In an embodiment, thenarrow contact pads 124B have a width in the range of 30 to 40 μm and apitch in the range of 50 to 60 μm.

Although FIG. 1B illustrates an embedded device 126 within a corelesspackage substrate 100B, embodiments of the present invention areapplicable to cored package substrates as well. For instance,embodiments of the present invention are applicable to a cored packagesubstrate with an embedded device 126 having wide and narrow contactpads 124A and 124B on the top side 112 and wide and narrow contact pads122A and 122B on the bottom side 110. The top and bottom solder resistlayers 116 and 114 are formed on the top and bottom sides 112 and 110,respectively. The cored package substrate includes a stiffening coredisposed within the build-up structure 102.

It is to be appreciated that although FIGS. 1A and 1B illustrate contactpads with two different widths on each side of the coreless packagesubstrate, embodiments are not so limited. For instance, the firstand/or second of pads 122, 124 may include three or more sets of contactpads where each set has a different width. Each set may include one ormore contact pads that are arranged to correspond with a specificcontact pitch.

FIG. 2 illustrates a package assembly 200 including the coreless packagesubstrate 100B according to embodiments of the invention. The corelesspackage substrate 100B includes the build-up structure 102 and the topand bottom solder resist layers 116 and 114. In an embodiment, devicecomponents 202 are coupled to the top side 112 of the coreless packagesubstrate 100B. The top contact pads 124 may electrically couple to thedevice components 202 by interconnects 208A. The device components 202may be an integrated circuit die, a CPU, a memory chip, and/or agraphics processor. In an embodiment, at least one device component 202is an integrated circuit die that is flip-chip bonded to the corelesspackage substrate 100B. The embedded device 126 may be included in thebuild-up structure 102 of the coreless package substrate 100B. In anembodiment, the device components 202 are electrically coupled to theembedded device 126 by the narrow contact pads 124B. In an embodiment,the top solder resist layer 116 is disposed between the devicecomponents 202 and the build-up structure 102. In an embodiment, the topsolder resist layer 116 is disposed within an entire die shadow region(i.e., the regions directly underneath) of each device component 202.

In an embodiment, an SLI structure 206 is coupled to the bottom side 110of the coreless package substrate 100B. The SLI structure 206 may be anysuitable structure such as, but not limited to, an interposer or acircuit board. The wide contact pads 122A of the coreless packagesubstrate 100B may electrically couple to the SLI structure 206 byinterconnects 208B. According to embodiments of the invention,active/passive device components 204 are also coupled to the bottom side110 of the coreless package substrate 100B. The narrow contact pads 122Bof the coreless package substrate 100B may electrically couple to theactive/passive device components 204 by the interconnects 208C. In anembodiment, the bottom solder resist layer 114 is disposed between theactive/passive device components 204 and the build-up structure 102. Thebottom solder resist layer 114 may be disposed within an entire dieshadow region of each active/passive device component 204. Theinterconnects 208A-208C may be any suitable interconnect structureformed of any suitable interconnect material. In an embodiment, theinterconnects 208A-208C are solder bumps.

FIGS. 3A-3I illustrate a method of forming a coreless package substrateby forming a bottom solder resist layer before removing a temporarysubstrate, in accordance with an embodiment of the invention. In FIG.3A, a patterned dry film resist (DFR) layer 306 is initially formed on atemporary substrate 302. In an embodiment, the temporary substrate 302is a rigid carrier substrate. The temporary substrate 302 provides arigid base upon which structures may form. In an embodiment, thetemporary substrate 302 is a panel containing multiple packagesubstrates. For instance, the temporary substrate 302 may be a panelcontaining an N×N array of package substrates. The temporary substrate302 may be formed of any well-known stiffening core. For example, thetemporary substrate 302 may be formed of a reinforced insulating layerdisposed between a pair of release layers and a pair of metal foillayers on top of the release layers.

In embodiments, the patterned DFR layer 306 exposes portions of a topsurface 303 of the temporary substrate 302. The exposed portions of thetop surface 303 allow structures to form on the temporary substrate 302.The patterned DFR layer 306 may be formed by first laminating a layer ofDFR on the temporary substrate 302 and subsequently patterning the DFRlayer to form openings 308. In an embodiment, the openings 308 areformed by any conventional exposure and developer process where exposureto electromagnetic radiation cross-links the DFR film and a developerremoves unexposed regions of the DFR film.

Next, in FIG. 3B, multi-layered structures 304 are formed on thetemporary substrate 302 within the openings 308. In an embodiment, eachmulti-layered structure 304 is formed of three layers: a bottom layer304A, a middle layer 304B, and a top layer 304C. In embodiments, the toplayer 304C of each multi-layered structure 304 is later used to form thebottom contact pads 122. In an embodiment, the top layer 304C is formedof a conductive material designed for use as the bottom contact pads122. For example, the top layer 304C may be formed of a metal, such ascopper. In an embodiment, the bottom layer 304A is formed of a samematerial as the metal foil in the temporary substrate 302. For example,the bottom layer 304A may be formed of copper. In an embodiment, thebottom layer 304A and the top layer 304C are formed of the sameconductive material. In a particular embodiment, the bottom layer 304Aand the top layer 304C are formed of copper. In embodiments, the middlelayer 304B is disposed between the bottom and top layers 304A and 304C.The middle layer 304B may be formed of a material different from thebottom and top layers 304A and 304C. In an embodiment, the middle layer304B is formed of a material that can be selectively removed relative tothe first and third layers 304A and 304C. For instance, the middle layer304B may be formed of nickel.

The multi-layered structures 304 may be formed by a series of anysuitable deposition techniques, such as chemical vapor deposition (CVD)or physical vapor deposition (PVD). In an embodiment, the multi-layeredstructures 304 are formed by initially depositing the first layer 304Aon top of the temporary substrate 302 as well as the patterned DFR layer306. Next, the second layer 304B is deposited on top of the first layer304A. Thereafter, the third layer 304C is deposited on top of the secondlayer 304B. Once all three layers are deposited, then the DFR layer 306is removed, along with portions of the first, second, and third layers304A, 304B, and 304C disposed on top of the DFR layer 306. As such, themulti-layered structures 304 remain on the temporary substrate 302 asillustrated in FIG. 3B.

Each multi-layered structure 304 may be designed to have a certain widthand pitch. In embodiments, the widths of the multi-layered structures304 define the width of the bottom contact pads 122. The pitch of themulti-layered structures 304 may also define the pitch of the bottomcontact pads 122. Accordingly, the pitch of the multi-layered structure304 may be designed to be compatible with contact pitches of a circuitboard or a device component. Therefore, each multi-layered structure 304may be designed to have wide or narrow widths as shown in FIG. 3B.

In FIG. 3B, the multi-layered structures 304 include wide multi-layeredstructures 304X and narrow multi-layered structures 304Y. In anembodiment, the wide multi-layered structures 304X are formed to have awidth W1 and a pitch P1. The width W1 and pitch P1 may correspond withcontact arrangements of an SLI structure such as a PCB. Accordingly, inan embodiment, the wide multi-layered structures 304X have a width W1 inthe range of 300 to 400 μm and a pitch P1 in the range of 600-800 μm.According to embodiments of the invention, the narrow multi-layeredstructures 304Y may be formed to have a width W2 corresponding tofine-pitches of active/passive device components, such as memory chipsor magnetic inducers. Such device components may require contact pitchesthat are significantly narrower than the contact pitch of circuitboards. In an embodiment, each narrow multi-layered structure 304Y has awidth W2 that is at least 3 times narrower than each wide multi-layeredstructure 304X. In a particular embodiment, each narrow multi-layeredstructure 304Y has a width W2 in the range of 80 to 100 μm and a pitchP2 in the range of 160 to 200 μm.

In FIG. 3C, a bottom solder resist layer 114 is then formed on exposedsurfaces of the temporary core 302 and the multi-layered structures 304by any suitable lamination technique, such as, but not limited to,silk-screening, spraying, or vacuum laminating. In an embodiment, thebottom solder resist layer 114 completely covers the exposed surfaces ofthe temporary core 302 and the multi-layered structures 304. In anembodiment, the bottom solder resist layer 114 is formed to a thicknesssufficient to substantially electrically isolate each pad of the bottomcontact pads 122. For example, the bottom solder resist layer 114 isformed to a thickness in the range of 25 to 45 μm. The bottom solderresist layer 114 may be formed of an insulating material that has poorwettability to paste materials, i.e., repels, or does not bond withpaste materials, such as solder paste. In an embodiment, the bottomsolder resist layer 114 is formed of a polymer. In an embodiment, thebottom solder resist layer 114 is formed of a polymer, such as an epoxyresin. Further, in an embodiment, the bottom solder resist layer 114 isformed as a photosensitive layer such that the bottom solder resistlayer 114 may be patterned by optical lithography. In such anembodiment, the bottom solder resist layer 114 is formed of a materialcontaining a photoactive package. In a particular embodiment, the bottomsolder resist layer 114 is formed of liquid photoimageable solder mask(LPSM) or dry film photoimageable solder mask (DFSM).

Next, in FIG. 3D, a bottommost insulating layer 104A is deposited on thebottom solder resist layer 114, thereby beginning formation of thebuild-up structure 102. The bottommost insulating layer 104A may beformed by any suitable lamination technique, such as vacuum lamination.In an embodiment, the bottommost insulating layer 104A does not makecontact with the top layer 304C of the stacked structures 304. Thebottommost insulating layer 104A may be formed to have a thickness t1sufficient to substantially prevent electrical interference betweenstructures above and below the bottommost insulating layer 104A. In anembodiment, the bottommost insulating layer 104A may have a thickness t1ranging from 35 to 55 μm. In an embodiment, the bottommost insulatinglayer 104A is formed of an epoxy-based resin with a silica filler toprovide suitable mechanical properties that meet reliabilityrequirements of the coreless package substrate. In a particularembodiment, the bottommost insulating layer 104A is formed of AjinomotoBuild-up Film (ABF).

Thereafter, in FIG. 3E, openings 314 may be formed in the bottommostinsulating layer 104A and the bottom solder resist layer 114 to exposethe top layer 304C of each multi-layered structure 304. The openings 314may be formed by any suitable etching technique, such as laser ablation.In an embodiment, forming the openings 314 by laser ablation removes aportion of the top layer 304C as shown in FIG. 3E. Each opening 314allows a conductive structure, such as a via 108 as depicted in FIG. 3F,to connect to the top layer 304C.

Next, in FIG. 3F, the via 108 and a conductive layer 106 is formed. Toform the via 108 and the conductive layer 106, a DFR layer may beinitially patterned on top of the bottommost insulating layer 104A. Thepatterned DFR layer may define the lateral boundaries of the conductivelayer 106. Thereafter, a conductive material may be deposited in theopening 314 and between the DFR layers with a single deposition process.In an embodiment, conductive material is deposited by electrolessplating. Once the conductive material is deposited, the DFR layer isremoved. The remaining conductive material disposed between the DFRlayer and within the openings 314 may form the vias 108 and conductivelayers 106.

The via 108 may be formed within the opening 314 such that the top layer304C of each multi-layered structure 304 is electrically coupled to theconductive layer 106. The conductive layer 106 may be one of severalredistribution layers for routing current through the build-up structure102 as shown in FIG. 3G. The conductive layer 106 and via 108 may beformed of any conductive material, such as a metal. In an exemplaryembodiment, the conductive layer 106 and via 108 are formed of copper.

The steps described in FIGS. 3D-3F above illustrate a semi-additiveprocess (SAP). The SAP may be repeated several times to form thebuild-up structure 102 shown at least in FIG. 3G. The build-up structure102 illustrated in FIG. 3G is formed of four SAPs. However, alternativeembodiments may use more or less iterations of SAPs to form the build-upstructure 102 for a coreless package substrate according to embodimentsof the invention. Although FIG. 3G does not illustrate an embeddeddevice (e.g., 126 in FIG. 1B) within the build-up structure 102,embodiments where an embedded device is formed within the build-upstructure 102 are contemplated. The embedded device 126 may be formedwithin the build-up structure 102 before or after any SAP iteration. Inembodiments, the build-up structure 102 does not contain a stiffeningcore.

The build-up structure 102 has a top side 112 and a bottom side 110. Theconductive layers 106 may be redistribution layers that allow variousinterconnections between the top contact pads 124 and the bottom contactpads 122 (i.e., the top layers 304C of the multi-layered structures304). In an embodiment, the build-up structure 102 only includesmaterials used for the sole purpose of forming the build-up structure.For instance, the build-up structure 102 may include materials forbarrier layers, seed layers, and any other similar materials used toform the insulating layers 104, conductive layers 106, and vias 108.Other materials used for purposes of stiffening the build-up structure102 are not included in the build-up structure 102. For instance, astiffening structure formed of a pre-preg reinforced with glass fibers,or any other suitable stiffening material, are not included in thebuild-up structure 102. In an embodiment, the build-up structure 102 iscompletely formed of only two materials: the material used to form theinsulating layers 104 and the material used to form the conductivelayers 106 and vias 108. Accordingly, in a specific embodiment, thebuild-up structure 102 contains only ABF and copper.

In embodiments, a last SAP forms the top contact pads 124. The topcontact pads 124 may be disposed on top of the topmost insulating layer104D such that the top contact pads 124 are entirely above the topmostinsulating layer 104D. The top contact pads 124 are coupled to the vias108 and the conductive layers 106 so that current may flow into and outof the top contact pads 124. In embodiments, the top side 112 of thebuild-up structure 102 makes electrical connection with devicecomponents. As such, the top contact pads 124 may be designed to have awidth and a pitch compatible with fine contact pitches of devicecomponents. For example, the top contact pads 124 may have a widthbetween 80 to 90 μm and a pitch between 120 to 130 μm. Although shownwith only one top contact width and pitch, the top contact pads 124 mayinclude wide and narrow contact pads as discussed in FIG. 1B. Forinstance, the top contact pads 124 may have narrow pads with a width inthe range of 30 to 40 μm and a pitch in the range of 50 to 60 μm. Thetop contact pads 124 may be formed of any suitable conductive material.In an embodiment, the top contact pads 124 are formed of a metal, suchas copper.

Next, in FIG. 3H, a top solder resist layer 116 is formed on the topside 112 of the build-up structure 102. Formation of the top solderresist layer 116 may be according to the same material, technique, andthickness as the bottom solder resist layer 114. In an embodiment, thetop solder resist layer 116 is initially formed on exposed surfaces ofthe topmost insulating layer 104D and the top contact pads 124. Openings316 are subsequently formed in the top solder resist layer 116 to exposethe top contact pads 124 by any suitable exposure and develop techniquewell known in the art. The openings 316 allow interconnect structures,such as solder bumps, to be formed within the openings 316. As such, theinterconnect structures may allow the top contact pads 124 to be coupledto device components, such as device components 202 in FIG. 2. Remainingportions of the top solder resist layer 116 may electrically isolateeach contact pad of the top contact pads 124 and may resist formation ofsolder residue between each contact pad of the top contact pads 124.

Next, in FIG. 3I, the temporary substrate 302 shown in FIG. 3H, as wellas the first and second layers 304A and 304B of the multi-layeredstructures 304, are removed, thereby forming a coreless packagesubstrate 300 with dual solder resist layers according to an embodimentof the invention. In an embodiment, the temporary substrate 302 isremoved by selectively etching the release layer relative to the metalfoil and the reinforced insulating layer of the temporary substrate 302.Next, the metal foil is removed along with the first layer 304A of themulti-layered structure 304. In an embodiment, the metal foil and thefirst layer 304A are made of the same material, such as copper. As such,the metal foil and the first layer 304A may be removed by an etchantselective to copper. In an embodiment, the second layer 304B preventsfurther etching by the etchant. Accordingly, in an embodiment, thesecond layer 304B is an etch stop layer. The second layer 304B may beformed of nickel. Thereafter, the second layer 304B is selectivelyremoved relative to the third layer 304C and the bottom solder resistlayer 114. As a result, the third layer 304C may remain as the bottomcontact pads 122 at a bottom of pockets 318. The pockets 318 may allowinterconnect structures, such as solder bumps, to electrically couple tothe bottom contact pads 122. The interconnect structures may couple thebottom contact pads 122 to device components and/or circuit boards.

As shown in FIG. 3I, the coreless package substrate 300 includes thebuild-up structure 102, the bottom solder resist layer 114, and the topsolder resist layer 116. In an embodiment, a portion of the bottomsolder resist layer 114 is disposed between each contact pad of thebottom contact pads 122 and the bottommost insulating layer 104A. Thebottom solder resist layer 114 may be disposed an entire distancebetween the bottom contact pads 122 and the bottommost insulating layer104A. In an embodiment, the bottommost insulating layer 104A does notmake contact with the bottom contact pads 122. The bottom solder resistlayer 114 may be disposed on sidewalls of the bottom plurality of pads122. Furthermore, the bottom solder resist layer 114 may also bedisposed on the internal surfaces of the bottom contact pads 122. In anembodiment, the bottom solder resist layer 114 is not formed on theexternal surface of the bottom contact pads 122.

FIGS. 4A-4H illustrate a method of forming a coreless package substrateby forming a bottom solder resist layer after removing a temporarysubstrate, in accordance with an embodiment of the invention. Techniquesand materials used to form the coreless package substrate in FIGS. 4A-4Hare similar to those discussed above in FIGS. 3A-3I. As such, thetechniques and materials are not as thoroughly described in thediscussion of the method illustrated in FIGS. 4A-4H. If desired, thedetails of such materials and techniques may be referenced from thediscussion of FIGS. 3A-3I.

In FIG. 4A, a patterned DFR layer 306 is formed on a temporary substrate302. The patterned DFR layer 306 exposes portions of a top surface 303of the temporary substrate 302. The exposed portions of the top surface303 allow structures to form on the temporary substrate 302. Next, asshown in FIG. 4B, bottom contact pads 122 are formed on the exposedportions of the temporary substrate 302. Each contact pad 122 may bedesigned to have a width according to contact pitches of a circuit boardor a device component. In an embodiment, the bottom contact pads 122includes wide contact pads 122A and narrow contact pads 122B. The widecontact pads 122A may be formed to have a width W1 corresponding to widecontact pitches of a circuit board, such as a PCB. Accordingly, in anembodiment, each wide contact pad 122A has a width W1 in the range of300 to 400 μm. According to embodiments of the invention, the narrowcontact pads 122B may be formed to have a width W2 compatible withactive/passive device components, such as memory chips or magneticinducers. In an embodiment, each narrow contact pad 122B has a width W2that is at least 5 times smaller than each wide contact pad 122A. In aparticular embodiment, each narrow contact pad 122B has a width W2 inthe range of 40 to 60 μm.

Next, the build-up structure 102 is formed by iterative SAPs as shown inFIG. 4C. The build-up structure 102 is formed of vias 108, conductivelayers 106, and insulating layers 104A, 104B, and 104C. A top and bottomcontact pads 124 and 122 may be formed on a top and bottom side 112 and110 of the build-up structure, respectfully. The top contact pads 124may be formed on a top surface of a topmost insulating layer 104C.

Thereafter, in FIG. 4D, a top solder resist layer 116 is laminated on atop side 112 of the build-up structure 102. The top solder resist layer116 has a top surface 402. Openings 316 are subsequently formed in thetop solder resist layer 116 to expose the top contact pads 124. In anembodiment, the openings 316 allow interconnect structures, such assolder bumps, to be formed in the openings 316. The interconnectstructures may electrically couple the top contact pads 124 to devicecomponents, such as device components 202 in FIG. 2. The top solderresist layer 116 may prevent bridging between the contact pads 124 byrepelling solder-based materials during formation of the interconnectstructures.

Next, in FIG. 4E, the temporary substrate 302 is removed from thebuild-up structure 102 to expose the bottom side 110 and the bottomcontact pads 122 of the build-up structure 102. In an embodiment wherethe temporary substrate 302 is a panel of an N×N array of packages, thebuild-up structure 102 is de-paneled from the temporary substrate 302.Once the temporary substrate 302 is removed, the remaining structure 401may be extremely pliable due to a lack of a stiffening structure (i.e.,the temporary substrate 302). For subsequent processing to occur, theremaining structure 401 needs to be placed on a stiff structure. Forinstance, as shown in FIG. 4F, the build-up structure 102 may beinverted and planarized by a planarization structure 403. In anembodiment, the top surface 402 of the top solder resist layer 116 isplaced upon the planarization structure 403 to expose the bottom side110 of the build-up structure 102 upward. The planarization structure403 substantially planarizes the build-up structure 102 and provides arigid base for further processing. In an embodiment, the planarizationstructure 403 is a vacuum fixture. The planarization structure 403 maydraw the build-up structure 102 into a planarized position with suctionforce applied by the planarization structure 403.

In FIG. 4G, the bottom solder resist layer 114 is then laminated on thebottom side 110 of the build-up structure 102, and openings 404 aresubsequently formed in the bottom solder resist layer 114 to expose thebottom contact pads 122. In an embodiment, the openings 404 allowinterconnect structures, such as solder bumps, to be formed within theopenings 404. The interconnect structures may electrically couple thebottom contact pads 122 to device components (e.g., active/passivedevice components 204 in FIG. 2) and/or a circuit board (e.g., SLIstructure 206 in FIG. 2).

Thereafter, in FIG. 4H, the build-up structure 102 is removed from theplanarization structure 403 to form the coreless package substrate 400,according to an embodiment of the invention. The coreless packagesubstrate 400 may now be implemented in a package assembly. Asillustrated in FIG. 4H, the coreless package substrate 400 has beeninverted back to its orientation before being placed on theplanarization structure 403. In embodiments, each contact pad of thebottom contact pads 122 does not extend above the bottommost insulatinglayer 104A. In an embodiment, a portion of the bottom solder resistlayer 114 is on top of a portion of the bottom contacts 122. In anembodiment, a portion of the top solder resist layer 116 is disposeddirectly laterally adjacent to each contact pad of the top contact pads124. Additionally, in an embodiment, no portion of the bottom solderresist layer 114 is disposed directly laterally adjacent to each contactpad of the bottom contact pads 122. The top and bottom solder resistlayers 116 and 114 prevent bridging between two adjacent contact pads ofthe top and bottom contact pads 124 and 122, respectively, from solderpaste residue. Accordingly, the solder resist layers 114 and 116 allownarrow contact pads to be formed on both sides of the coreless packagesubstrate to couple with fine-pitched device components.

FIGS. 5A-5G illustrate a method of forming surface finishes on contactpads located on both sides of a coreless package substrate, inaccordance with an embodiment of the invention. Having solder resistlayers on both sides of a coreless package substrate allows a surfacefinish on the bottom side of the coreless package substrate to have adifferent thickness than a surface finish on the top side of thecoreless package substrate.

In FIG. 5A, a coreless package substrate 500 is provided. The packagesubstrate 500 may be formed by either method described above in FIGS.3A-3I and FIGS. 4A-4H, but is shown as being formed by the methoddescribed in FIGS. 4A-4H. The coreless package substrate 500 includes abuild-up structure 102 and a top and bottom contact pads 124 and 122.The top contact pads 124 are disposed on a top side 112 of the build-upstructure 102, and the bottom contact pads 122 are disposed on a bottomside 110 of the build-up structure 102. In an embodiment, the topcontact pads 124 includes wide contact pads 124A and narrow contact pads122B, and the bottom contact pads 122 includes wide contact pads 122Aand narrow contact pads 122B. The narrow contact pads 124B of the topcontact pads 124 may be electrically coupled to an embedded device 126located within the build-up structure 102. A top solder resist layer 116is disposed on the top side 112 of the build-up structure 102, and abottom solder resist layer 114 is disposed on the bottom side 110 of thebuild-up structure 102.

Next, in FIG. 5B, one side of the coreless package substrate 500 iscovered with a temporary protective layer 502. In the embodimentdepicted in FIG. 5B, the top side 112 is covered with the temporaryprotective layer 502. The temporary protective layer 502 may cover allexposed surfaces of structures on the top side 112 to expose structuresonly on the bottom side 110. The temporary protective layer 502 mayprevent deposition of a surface finish on the top contact pads 124. Inan embodiment, the temporary protective layer 502 is formed of anysuitable insulating material resistant to chemical reactions duringdeposition of a surface finish. In a particular embodiment, thetemporary protective layer 502 is formed of polyethylene terephthalate(PET).

Thereafter, in FIG. 5C, a bottom surface finish 118 is formed on exposedsurfaces of the bottom contact pads 122. The bottom surface finish 118passivates the bottom contact pads 122 to prevent oxidation of thebottom contact pads 122. In an embodiment, the bottom surface finish 118is formed of two layers: a first bottom surface finish 118A and a secondbottom surface finish 118B. In an embodiment, the first bottom surfacefinish 118A is formed on the bottom contact pads 122, and the secondbottom surface finish 118B is formed on the first bottom surface finish118A. The first and second bottom surface finishes 118A and 118B may beformed by any suitable deposition technique, such as electrolessplating. In an embodiment, the first bottom surface finish 118A isformed to a thickness sufficient to adhere the second bottom surfacefinish 118B to the bottom contact pads 122. In a particular embodiment,the first bottom surface finish 118A is formed to a thickness rangingfrom 6 to 8 μm. In an embodiment, the second bottom surface finish 118Bis formed to a thickness sufficient to prevent oxidation of the firstbottom surface finish 118A. In a particular embodiment, the secondbottom surface finish 118B is formed to a thickness ranging from 2 to 4μm. In an embodiment, the first and second bottom surface finishes 118Aand 118B are formed of a conductive material, such as a metal containingnickel (Ni), palladium (Pd), gold (Au), silver (Ag), and combinationsthereof. In a particular embodiment, the first bottom surface finish118A is formed of Ni, and the second bottom surface finish 118B isformed of PdAu.

After the bottom surface finish 118 is formed, the temporary protectivelayer 502 is removed, as illustrated in FIG. 5D. Removing the temporaryprotective layer 502 exposes the top solder resist layer 116 as well asportions of the top contact pads 124. In embodiments, the bottom surfacefinish 118 remains on the bottom contact pads 122.

Next, in FIG. 5E, a temporary protective layer 504 is formed on thebottom side 110 to cover exposed surfaces of the bottom solder resistlayer 114 and the bottom surface finish 118. The temporary protectivelayer 504 may cover all exposed surfaces of structures on the bottomside 110 to expose structures only on the top side 112. In anembodiment, the temporary protective layer 504 is formed of any suitablechemically resistant insulating material, such as polyethyleneterephthalate (PET). The temporary protective layer 504 may preventdeposition of a surface finish on the bottom surface finish 118.

Thereafter, in FIG. 5F, a top surface finish 120 is formed on exposedsurfaces of the top contact pads 124. The top surface finish 120 may beused to electrically couple the top contact pads 124 to devicecomponents 202 shown in FIG. 2. In an embodiment, the top surface finish120 is formed of two layers: a first top surface finish 120A and asecond top surface finish 120B. In an embodiment, the first top surfacefinish 120A is formed on the top contact pads 124 and on a portion ofthe top solder resist layer 116, and the second top surface finish 120Bis formed on the first top surface finish 120A. The first and second topsurface finishes 120A and 120B may be formed by any suitable depositiontechnique, such as electroless plating.

In an embodiment, the first top surface finish 120A is formed to athickness at least three to four times larger than the thickness of thefirst bottom surface finish 118A. In a particular embodiment, the firsttop surface finish 120A is formed to a thickness ranging from 25 to 30μm. In an embodiment, the second top surface finish 120B is formed to athickness sufficient to prevent oxidation of the first top surfacefinish 120B. In a particular embodiment, the second top surface finish120B is formed to a thickness ranging from 2-4 μm.

In an embodiment, the first and second top surface finishes 120A and120B are formed of a conductive material, such as a metal Ni, Pd, Au,Ag, and combinations thereof. In a particular embodiment, the first topsurface finish 120A is formed of Ni and the second top surface finish120B is formed of PdAu. In an embodiment, the first top surface finish120A is formed to a thickness sufficient to electrically couple the topcontact pads 124A and 124B to device components. The first top surfacefinish 120A may be formed to a thickness such that the first top surfacefinish 120A extends beyond a top surface 117 of the top solder resistlayer 116. In an embodiment, the first top surface finish 120A extendsabove the top surface 117 to make electrical connection with contacts ofthe device component 202, such as a memory chip or any other integratedcircuit device. Micro bumps may therefore not be needed to form anelectrical connection between the device component 202 and the topcontact pads 124.

After the top surface finish 120 is formed, the temporary protectivelayer 504 is removed, as illustrated in FIG. 5G, thereby forming acoreless package substrate 500 with top and bottom surface finishes 120and 118. Having solder resist layers on both sides of the corelesspackage substrate enables the method described in FIGS. 5A-5G of formingsurface finishes with different thicknesses.

While the above method discussed in FIGS. 5A-5G describe application ofthe bottom surface finish 118 on the bottom contact pads 122 followed byapplication of the top surface finish 120 on the top contact pads 124,this method may be performed in the opposite order as well. For example,the top surface finish 120 may be applied to the top contact pads 124followed by application of the bottom surface finish 118 on the bottomcontact pads 122.

FIG. 6 illustrates a computing system 600 implemented with oneimplementation of the invention. The computing device 600 houses a board602. The board 602 may include a number of components, including but notlimited to a processor 604 and at least one communication chip 606. Theprocessor 604 is physically and electrically coupled to the board 602.In some implementations the at least one communication chip 606 is alsophysically and electrically coupled to the board 602. In furtherimplementations, the communication chip 606 is part of the processor604.

Depending on its applications, computing device 600 may include othercomponents that may or may not be physically and electrically coupled tothe board 602. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth).

The communication chip 606 enables wireless communications for thetransfer of data to and from the computing device 600. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 606 may implement anyof a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3I, 4G, 5G, andbeyond. The computing device 600 may include a plurality ofcommunication chips 606. For instance, a first communication chip 606may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 606 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 604 of the computing device 600 includes an integratedcircuit die packaged within the processor 604. In some implementationsof the invention, the integrated circuit die is mounted on a packagesubstrate, such as a coreless package substrate with dual side solderresist layers, that is formed in accordance with implementations of theinvention. The term “processor” may refer to any device or portion of adevice that processes electronic data from registers and/or memory totransform that electronic data into other electronic data that may bestored in registers and/or memory.

The communication chip 606 also includes an integrated circuit diepackaged within the communication chip 606. In accordance with anotherimplementation of the invention, the integrated circuit die is mountedon a package substrate, such as a coreless package substrate with dualside solder resist layers, that is formed in accordance withimplementations of the invention.

In further implementations, another component housed within thecomputing device 600 may contain an integrated circuit die that ismounted on a package substrate, such as a coreless package substratewith dual side solder resist layers, that is formed in accordance withimplementations of the invention.

In various implementations, the computing device 600 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 600 may be any other electronic device that processes data.

In an embodiment, a package substrate includes a build-up structurecomprising at least one insulating layer, at least one via, and at leastone conductive layer, a first plurality of contact pads on a first sideof the build-up structure, a second plurality of contact pads on asecond side of the build-up structure opposite of the first side, afirst solder resist layer on the first side; and a second solder resistlayer on the second side, the first and second solder resist layerscovering all exposed surfaces of the first and second sides of thebuild-up structure, respectively.

The build-up structure may not include a stiffening core. In anembodiment, the first solder resist layer is disposed an entire distancebetween the first plurality of contact pads and a bottommost insulatinglayer of the at least one insulating layer. The first solder resistlayer may be disposed on sidewalls of the first plurality of contactpads. The first solder resist layer may be disposed on an internal sideof the first plurality of contact pads. In an embodiment, the firstsolder resist layer is not disposed on an external side of the firstplurality of contact pads. Additionally, in an embodiment, the firstplurality of contact pads includes first wide contact pads and firstnarrow contact pads, the first wide contact pads having a pitch greaterthan the first narrow contact pads. The package substrate may alsoinclude a device embedded within the coreless package substrate. In anembodiment, the package substrate also includes a stiffening coredisposed within the build-up structure. The second plurality of contactpads may include second wide contact pads and second narrow contactpads, the second wide contact pads having a pitch greater than thesecond narrow contact pads. In an embodiment, the first solder resistlayer is not directly laterally adjacent to the first plurality ofcontact pads, and wherein the second solder resist layer is directlylaterally adjacent to a portion of the second plurality of contact pads.Additionally, in an embodiment, the first solder resist layer is on aportion of the first plurality of contact pads. The second solder resistlayer may be disposed on all exposed top surfaces of a topmostinsulating layer of the at least one insulating layer.

In an embodiment, a method of forming a package substrate includesforming a plurality of multi-layered structures on a top surface of atemporary substrate, forming a first solder resist layer on exposedsurfaces of the temporary substrate and the plurality of multi-layeredstructures, forming a build-up structure comprising least one insulatinglayer, a plurality of vias, and at least one conductive layer on thefirst solder resist layer, wherein a top conductive layer forms a secondplurality of contact pads on a top surface of a topmost insulatinglayer, forming a second layer of solder resist on a top surface of thetopmost insulating layer, exposing at least a portion of the secondplurality of contact pads, and removing the temporary substrate and aportion of each multi-layered structure of the plurality ofmulti-layered structures, a remaining portion of each multi-layeredstructure forming a first plurality of contact pads.

Forming the build-up structure may include a semi-additive process. Inan embodiment, forming the build-up structure further includes placing adevice within the at least one insulating layer and at least oneconductive layer such that the device is embedded within the build-upstructure. Forming the build-up structure may also include etchingthrough a portion of the first solder resist layer to expose theplurality of multi-layered structures. In an embodiment, forming theplurality of multi-layered structures includes forming a patterned dryfilm resistor layer on top of the temporary substrate, depositing afirst layer on the patterned dry film resistor and on a top surface ofthe temporary substrate, depositing a second layer on top of the firstlayer, depositing a third layer on top of the second layer, and removingthe patterned dry film resistor layer along with portions of the first,second, and third layers disposed on top of the patterned dry filmresistor layer. Third layer may remain as the first plurality of contactpads following removal of the dry film resistor layer.

In an embodiment, a method of forming a package substrate includesproviding a temporary substrate, forming a first plurality of contactpads on a top surface of the temporary substrate, forming at least oneinsulating layer and at least one conductive layer on the firstplurality of contact pads, wherein a top conductive layer forms a secondplurality of contact pads on a top surface of a topmost insulatinglayer, forming a first layer of solder resist on the top surface of thetopmost insulating layer, exposing at least a portion of the secondplurality of contact pads, removing the temporary substrate to expose abottom surface of the bottommost insulating layer, temporarilyplanarizing the intermediate structure, and forming a second layer ofsolder resist on the bottom surface of the bottommost insulating layer,exposing at least a portion of the first plurality of contact pads.

Forming the first plurality of contact pads may include forming apatterned dry film resistor layer on top of the temporary substratedepositing a conductive layer on the patterned dry film resistor and ona top surface of the temporary substrate, and removing the patterned dryfilm resistor layer along with portions of the conductive layer disposedon top of the patterned dry film resistor layer such that left overportions of the conductive layer remain to form the first plurality ofcontact pads. In an embodiment, temporary flattening the intermediatestructure includes inverting the intermediate structure and placing theintermediate structure on a vacuum fixture. In an embodiment, invertingthe intermediate structure causes the bottom surface of the bottommostinsulating layer to be exposed upward.

In an embodiment, a method of forming surface finishes on a packagestructure includes providing a coreless package substrate having a firstside and a second side opposite of the first side, the coreless packagesubstrate comprising a single build-up structure comprising at least oneinsulating layer, at least one via, and at least one conductive layer, afirst plurality of contact pads on the first side, and a secondplurality of contact pads on the second side, a first solder resistlayer on the first side, and a second solder resist layer on the secondside, forming a first protection layer on the first side of the corelesspackage substrate and depositing a bottom surface finish on the secondplurality of contact pads, the bottom surface finish having a firstthickness, removing the first protection layer from the first side ofthe coreless package substrate to expose one or more contact padsdisposed on the first side, forming a second protection layer on thesecond side of the coreless package substrate and depositing a topsurface finish on the first plurality of contact pads, the top surfacefinish having a second thickness different than the first thickness, andremoving the second protection layer from the second side of thecoreless package substrate.

At least one of the bottom surface finish and the top surface finish mayextend above a top surface of the first solder resist layer and thesecond solder resist layer, respectively. In an embodiment, depositing abottom surface finish and a top surface finish includes depositing afirst conductive material and a second conductive material directly onthe first conductive material. In an embodiment, depositing the firstand second conductive materials include electroless plating. The firstconductive material may include nickel. The second conductive materialmay include gold and palladium. In an embodiment, the second thicknessis a magnitude of three to four times a thickness of the firstthickness.

In utilizing the various aspects of this invention, it would becomeapparent to one skilled in the art that combinations or variations ofthe above embodiments are possible for forming a coreless packagesubstrate with dual solder resist layers. Although embodiments of thepresent invention have been described in language specific to structuralfeatures and/or methodological acts, it is to be understood that theinvention defined in the appended claims is not necessarily limited tothe specific features or acts described. The specific features and actsdisclosed are instead to be understood as particularly gracefulimplementations of the claimed invention useful for illustratingembodiments of the present invention.

What is claimed is:
 1. A method of forming a package substrate,comprising: providing a temporary substrate; forming a first pluralityof contact pads on a top surface of the temporary substrate, wherein thefirst plurality of contact pads has both wide and narrow contact pads;forming at least one insulating layer and at least one conductive layeron the first plurality of contact pads, wherein a top conductive layerforms a second plurality of contact pads on a top surface of a topmostinsulating layer, wherein the second plurality of contact pads has bothwide and narrow contact pads, and wherein the wide contact pads of thesecond plurality of contact pads are vertically over the wide contactpads of the first plurality of contact pads, and the narrow contact padsof the second plurality of contact pads are vertically over the narrowcontact pads of the first plurality of contact pads; forming a firstlayer of solder resist on the top surface of the topmost insulatinglayer, exposing at least a portion of the second plurality of contactpads; removing the temporary substrate to expose a bottom surface of abottommost insulating layer to form an intermediate structure;temporarily flattening the intermediate structure; and forming a secondlayer of solder resist on the bottom surface of the bottommostinsulating layer, exposing at least a portion of the first plurality ofcontact pads.
 2. The method of claim 1, wherein forming the firstplurality of contact pads comprises: forming a patterned dry film resistlayer on top of the temporary substrate; depositing a conductive layeron the patterned dry film resist and on a top surface of the temporarysubstrate; and removing the patterned dry film resist layer along withportions of the conductive layer disposed on top of the patterned dryfilm resist layer such that left over portions of the conductive layerremain to form the first plurality of contact pads.
 3. The method ofclaim 1, wherein temporary flattening the intermediate structurecomprises inverting the intermediate structure and placing theintermediate structure on a vacuum fixture.
 4. The method of claim 1,wherein the first plurality of contact pads has first pads having afirst pitch and second pads having a second pitch different than thefirst pitch, and wherein the second plurality of contact pads has firstpads having a first pitch and second pads having a second pitchdifferent than the first pitch.
 5. A method of forming a system,comprising: providing a temporary substrate; forming a first pluralityof contact pads on a top surface of the temporary substrate, wherein thefirst plurality of contact pads has both wide and narrow contact pads;forming at least one insulating layer and at least one conductive layeron the first plurality of contact pads, wherein a top conductive layerforms a second plurality of contact pads on a top surface of a topmostinsulating layer, wherein the second plurality of contact pads has bothwide and narrow contact pads, and wherein the wide contact pads of thesecond plurality of contact pads are vertically over the wide contactpads of the first plurality of contact pads, and the narrow contact padsof the second plurality of contact pads are vertically over the narrowcontact pads of the first plurality of contact pads; forming a firstlayer of solder resist on the top surface of the topmost insulatinglayer, exposing at least a portion of the second plurality of contactpads; removing the temporary substrate to expose a bottom surface of abottommost insulating layer; temporarily flattening an intermediatestructure; forming a second layer of solder resist on the bottom surfaceof the bottommost insulating layer, exposing at least a portion of thefirst plurality of contact pads; and subsequent to forming both thefirst layer of solder resist and the second layer of solder resist,coupling one of the first plurality of contact pads or the secondplurality of contact pads to a component having differing contact pitch,and coupling the other of the first plurality of contact pads or thesecond plurality of contact pads to a fine-pitch component and to aboard.
 6. The method of claim 5, wherein forming the first plurality ofcontact pads comprises: forming a patterned dry film resist layer on topof the temporary substrate; depositing a conductive layer on thepatterned dry film resist and on a top surface of the temporarysubstrate; and removing the patterned dry film resist layer along withportions of the conductive layer disposed on top of the patterned dryfilm resist layer such that left over portions of the conductive layerremain to form the first plurality of contact pads.
 7. The method ofclaim 5, wherein temporary flattening the intermediate structurecomprises inverting the intermediate structure and placing theintermediate structure on a vacuum fixture.